<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <ul id="parent">
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
    <script>
    /* firstchild --获取第一个子节点
      firstelementchild--获取第一个子元素节点
     */
     var parent=document.getElementById("parent");
     var first=parent.firshelementchild;
     if(first){
        //  chrome ie9以上
        first.style.color="red"
     }else{
        //  ie9 以下
        parent.firstchild.style.color="green";
     }
    </script>
</body>
</html>